A motor drive device has a drive circuit in which switching elements such as transistors are connected in series on the high potential side and on the low potential side. In the motor drive device, electric current is controlled by pulse width modulation (PWM) control. In the PWM control, while one of the switching elements is turned off, back electromotive force arises in a motor coil, and current flows in a free wheel diode disposed parallel to the other switching element.
JP S63-304715A (corresponding to U.S. Pat. No. 4,950,919) describes a synchronous rectification control to reduce loss of electric power that is caused by the current flowing in a free wheel diode. In the synchronous rectification control, while the current flows into the free wheel diode, a switching element having a low on-resistance and connected in parallel with the free wheel diode is made conducted.